This invention relates to coding and authentication, in particular, by identifying spectral emissions and a response to modulated excitation.
It is well known that valuable items, for example, negotiable instruments, works of art, etc. are susceptible to theft and counterfeiting.
With regard to documents, the advancement of color copier technology has made it fairly easy to create a color copy of any document, including currency, using commonly available equipment.
One way of protecting valuable items is to utilize the physical characteristics of the item itself as a way to identify the object. As an example, watermarks or signatures are typically produced by taking semantic information of the item to be protected, for example, alphanumeric characters, physical features, etc. or other related information (e.g. ownership information), as an input to a mathematical algorithm that generates a signature or watermark. These signatures or watermarks are typically kept with the item to be authenticated. For example, a digital watermark may be imbedded within digital information to be protected or it may be printed on or within an item that is valuable. In another example, the watermark or signature may be kept separate from the item, but when combined with the item to be authenticated produces proof of authentication. For instance, a smart card could be utilized that when read confirms certain physical characteristics about an item.
Objects and Advantages of the Invention
It is a first object and advantage of this invention to provide a system for coding and authenticating an item.
It is another object and advantage of this invention to code and authenticate an item by using a response to a specific periodic optical excitation.
The foregoing and other problems are overcome and the objects of the invention are realized by methods and apparatus in accordance with embodiments of this invention.
A method of coding and authentication includes the steps of irradiating a sample with a harmonically modulated radiation and detecting a component of an emission of the sample in response, where the component is out of phase with the radiation. The method further includes modulating the intensity of the radiation and identifying the sample by a phase difference between the radiation and the out of phase component.